The invention relates to a fluid-friction clutch or coupling for driving a vehicle radiator fan or the like and having a bimetallic strip mounted at a front side of a clutch housing for controlling a valve connection between clutch working an storage chambers in the housing.
A fluid-friction clutch of this type is known from German Patent (DE) No. 31 49 104 C2. A bimetallic strip is provided there which extends approximately diametrically over the circular area of the clutch housing and which engages, with its ends, in one recess respectively below radial ribs which are arranged only in the exterior area. The bimetallic strip is pressed into these recesses below the ribs by means of an elastic force which is applied by an actuating pin which projects into the housing interior and there presses on a valve lever which is either constructed to be elastic itself and tries to press the actuating pin toward the outside against the bimetallic strip, or which is loaded by a spring in the corresponding direction.
In the known construction, after the form-fitting locking-in of the ends of the bimetallic strip, a silicone stopper is pressed into each of the two fastening areas on both sides of the bimetallic strip. This stopper, because of its elastic characteristics, does not suppress the temperature-caused movement of the bimetallic strip, but provides that the bimetallic strip maintains its installed position. However, if clutches of the known construction, in an also known manner, are fastened directly to the front ends of crankshafts of engines, the danger exists, despite the securing by silicone stoppers, that as a result of shocks, this securing arrangement will open up, which may lead to wear at the bimetal fastening or also at the actuating pin. As a result, the adjusted connecting temperature of the clutch shifts in the direction of an early drive connection, which is undesirable. In addition, there is the danger that the clutch and therefore the radiator fan will fail.
An object of the invention is therefore to provide a secure and low-wear fastening of the bimetallic strip in a clutch of the above noted type.
In order to achieve this object, an arrangement is provided wherein a shoe constructed of material with good sliding characteristics is provided which is form fittingly slid onto a part of the cooling ribs, which shoe is interposed between projections on the ribs and the metallic strip to hold the bimetallic strip in position. By means of this construction, the bimetallic strip is held in a careful and low-wear fashion but will be secure in its position. Also in cases of high operational stress, particularly in commercial vehicles, no wear can therefore occur at the fastening. The adjusted connecting and disconnecting characteristics of the clutch are thus maintained.
Certain preferred embodiments provide for a slightly conical tapering shoe frame which is slidable on the ribs from the inside toward the outside and has the advantage that an easily mountable shoe is formed which can be slid on the ribs in a simple manner. A radial stop is provided on the shoe in certain preferred embodiments to precisely radially position the bimetallic strip end. Certain preferred embodiments provide that the bimetallic strip has bent tongues at its ends to circumferrentially position the bimetallic strip via engagement with the shoe which have the advantage that a securing of the bimetallic strip in circumferential direction is also achieved without any excessive local stress being exercised by pressure forces. Webs interconnecting ends of the cooling ribs over which the shoe is slidingly attached are provided in certain preferred embodiments to facilitate securing of the bimetallic strip in circumferential direction without stress. By means of these characteristics, it is achieved that the contact surface for the shoe at the ribs is relatively large so that the surface pressure remains low. Certain preferred embodiments include shoes with upper and lower transverse webs connected by lateral walls, the lower transverse web resting under the cooling rib end projection and on top of the bimetallic strip ends, to ensure that the large contact surface exists also between the shoe and the bimetallic strip. Preferred embodiments of the shoe have an upper transverse web which locks in behind a step at the cooling ribs to allow a simple fastening and securing of the shoe at the ribs. Especially preferred embodiments include a shoe made of a synthetic resin material such as TEFLON, proven to be particularly effective with respect to the manufacturing and the characteristic of the shoe.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.